Medical devices intended for implant into or for direct contact with the body of bodily tissues of a mammal (including a human), as for example medical prostheses or surgical implants, may be fabricated from a variety of materials including various metals, metal alloys, plastic or polymer materials, solid resin materials, glassy materials and other materials as may be suitable for the application and appropriately biocompatible. As examples, certain stainless steel alloys, cobalt-chrome alloys, polyethylene and other inert plastics have been used. Such devices include for example, without limitation, vascular stents, artificial joint prostheses, coronary pacemakers, implantable or contact lenses, etc. Often the native surface state of such a device has a wettability property that is other than ideal for the intended use. In such case it may be desirable to modify the wettability of at least a portion of such surfaces so as to make the surface wettability more suitable for the application or more suitable for other processing steps that ultimately make the surface more suitable for the application.
For example, in the case of an implantable vascular stent, it is often desirable to apply drugs to the surface of the stent prior to its introduction into a vascular vessel. When such drugs are applied in a liquid form, the wettability of the stent surface may affect the ability to apply a well-adhered drug layer. For another example, the degree of wettability of a surgical implant such as a joint prosthesis can affect the quality of lubrication that the joint enjoys after implant. As still another example, the wettability of a surface of a contact lens may affect the lubricity of the surfaces and the degree of wearer comfort.
Many materials have poorly wettable surfaces in their native states. Other materials have surfaces that become poorly wettable as a result of native oxides or other films that occur naturally after exposure to atmospheric conditions.
Many approaches have been applied in the past to affect the wettability of surfaces. These include the use of cleaning, including mechanical, ultrasonic, plasma, and chemical cleaning techniques. Other approaches have included the addition of surfactants or the application of films or coatings having different wettability characteristics. Often the cleaning and/or other measures have not been able to provide the desired results, or have been otherwise impractical, costly, undesirable, or ineffective. For many materials, cleaning alone is not adequate to provide wettability, since the native characteristics of the clean surface may not support wettability. For many materials, even an aggressive argon plasma surface cleaning does not provide suitable wettability of the material's surface.
Sometimes it is very useful that the wettability characteristics of a surface have a spatially variable quality. For example in the case of adhering a drug applied initially in a liquid form to surfaces of a surgically implantable medical device, it is sometimes useful to control the distribution of the drug on the surface so that portions of the surface have adhered drug, and other portions are substantially drug free—this may be done for therapeutic purposes or to minimize costs by not expending costly drugs on surface portions where there will be no useful effect.
Gas cluster ion beams are known, and have been used to process surfaces for purposes of cleaning, etching, smoothing, film growth, and the like. Gas cluster ions are ionized, loosely bound, aggregates of materials that are normally gaseous under conditions of standard temperature and pressure—typically consisting of from a few hundreds atoms or molecules to as many as a few ten thousands of atoms or molecules. Gas cluster ions can be accelerated by electric fields to considerable energies of thousands of keV. However because of the large number of atoms or molecules in each gas cluster ion, and because of the loose binding, their effect upon striking a surface is very shallow—the cluster is disrupted at impact and each atom or molecule carries only a few eV of energy. At the surface, instantaneous temperatures and pressures can be very high at gas cluster ion impact sites, and a variety of surface chemistry, etching, and cleaning effects can occur.
It is therefore an object of this invention to provide methods and systems for increasing the wettability of a surface of a medical device by the application of gas cluster ion beam technology.
Another object of this invention is to provide methods and systems for reducing the wettability of a surface of a medical device by the application of gas cluster ion beam technology.
Another object of this invention to provide methods and systems for modifying the wettability of a portion of a surface of a medical device in a controlled pattern by the application of gas cluster ion beam technology.
A still further object of this invention to provide methods and systems for improving the adherence of a coating originally applied in a fluid state to a surface of a medical device by improving the wettability of at least a portion of the surface by the application of gas cluster ion beam technology.